Corrugating apparatus

ABSTRACT

Corrugating apparatus that includes paddles and an ultrasonic welding device. The paddles are attached at one end to a belt that moves about a path. The paddles extend radially from the belt, and each paddle has a free end that supports a web as the paddles move about the path. The free ends of the paddles are able to move towards each other to cause the web to corrugate. The ultrasonic welding device is located downstream to where the paddles&#39; free ends move towards each other. The ultrasonic welding device has a horn and an anvil, and the anvil includes the free ends of the paddles.

This is a division of application Ser. No. 08/093,398 filed Jul. 19,1993 U.S. Pat. No. 5,612,127 which is a continuation-in-part ofapplication Ser. No. 07/925,384 filed Aug. 4, 1992, now abandoned, thedisclosures of which are incorporated here by reference.

TECHNICAL FIELD

This invention relates to (i) a composite structure containing acorrugated, nonwoven web of polymeric microfiber; (ii) afibrous-filtration-face-mask (hereinafter face mask) having a corrugatedfiltration layer, (iii) thermal insulation that includes a corrugated,nonwoven web of polymeric microfiber; (iv) a filter for removingparticulate and gaseous contaminants from a fluid; (v) a method ofmaking a corrugated, nonwoven web of polymeric microfiber; and (vi) acorrugating apparatus.

BACKGROUND OF THE INVENTION

Corrugated Microfiber Webs

Corrugated and pleated webs of polymeric microfiber are known in the artand have been disclosed in the following U.S. Pat. Nos. 5,038,775,4,939,016, 4,910,064, 4,842,739, 4,826,642, 4,774,001, 4,759,782,4,676,807, and 4,617,124.

U.S. Pat. No. 5,038,775 discloses a filter assembly that includes apleated microfibrous web as a filter medium. The filter medium ismaintained in a pleated condition by a scrim that extends over theupstream and downstream sides of the pleated filter medium to providesubstantially continuous support to the filter medium.

U.S. Pat. No. 4,939,016 discloses a composite web material that includesa hydraulically entangled laminate of melt blown microfibers and afurther layer, preferably at least one of pulp fibers, staple fibers,melt blown fibers, and continuous filaments, with or without particulatematerial. The patent discloses that this composite web can be formedinto a corrugated stretchable fabric by pre-stretching the web andhydraulically entangling the web while stretched.

U.S. Pat. No. 4,910,064 discloses a nonwoven web that has a multiplicityof substantially longitudinally molecularly oriented continuousfilaments of a thermoplastic polymer. Onto the longitudinal continuousfilaments are deposited a multiplicity of melt blown fibers having fiberdiameters of 0.5 to 50 micrometers (μm). The melt blown fibers formbonds at some of their intersections with the longitudinal continuousfilaments to stabilize and fix the orientation of those filaments. Thestabilized continuous filaments are pleated or corrugated and arestabilized in that condition by depositing a layer of melt blown fiberson one side of the pleats or corrugations (column 26, lines 12-16).

U.S. Pat. No. 4,842,739 discloses a high surface area filter cartridgethat contains a nested arrangement of disk-shaped filter layers. Thedisk-shaped filter layers have a pattern of regular radial pleats andcomprise a laminate that includes an upstream prefilter layer, afiltration media, and a downstream cover layer. The filtration media canbe a nonwoven web of melt blown microfibers. The filter laminate ispleated by an embossing operation.

U.S. Pat. Nos. 4,826,642 and 4,774,001 disclose a composite structurethat is useful as a flat filtration medium or as a pleated (corrugated)filtration structure. The composite structure comprises a microporousmembrane and a synthetic thermoplastic web of microfibers secured to themicroporous membrane by melt blowing the microfibers thereon.

U.S. Pat. Nos. 4,759,782 and 4,676,807 disclose a cylindrical filterstructure that may comprise a single pleated filter medium supported byan outer perforated, cylindrical support cage. The filter media maycomprise organic melt blown microfibers. In Example 1, a composite,cylindrical pleated filter structure was prepared from two layers ofmelt-blown polyester fibrous material having two glass fiber layerssandwiched therebetween. The melt-blown polyester fibrous materialcontained fibers having diameters ranging from 35 to 50 μm, and wascalendared to a thickness of 0.009 inches (pore size was 100 μm) beforebeing combined with the glass fiber medium. The composite structure wasplaced in pleated form in a perforated polypropylene cage. No disclosureis provided as to how the composite structure is pleated.

U.S. Pat. No. 4,617,124 discloses a polymeric, microfibrous filter sheetwhere the microfiber is coated with a cured thermosetting binding resinor polymer. In column 24, lines 29-31, it is disclosed that the filtersheet can be placed in pleated form and incorporated into a cartridge.

Face Masks

Nonwoven webs of polymeric microfiber have been commonly used in facemasks as filtration layers. U.S. Pat. Nos. 4,807,619, 4,536,440,4,215,682, and 3,802,429 disclose cup-shaped face masks that havenonwoven webs of polymeric microfiber as filtration layers.

Face masks have been disclosed that have corrugated or pleated surfaces.U.S. Pat. Nos. 4,807,619, 4,641,645, 4,536,440, 4,248,220, 3,985,132,3,220,409, and EP-A 0,149,590 A3 disclose such face masks. Of thesepatents, only U.S. Pat. No. 4,641,645, however, discloses a filter thatincludes a corrugated nonwoven web of polymeric microfiber. In U.S. Pat.No. 4,641,645, the face mask has a middle layer of polymeric microfiberdisposed coextensively between two polyester nonwoven webs. All threelayers are assembled into a composite mat and molded into a cup-shapedconfiguration having a plurality of tightly-compacted rib elements.While the tightly-compacted rib elements have peaks and valleys thatprovide the face mask with a corrugated effect, the tightly-compactedrib elements are employed to give the face mask structural strength (notto improve filtration performance), and they reduce the loftiness of themiddle layer of polymeric microfiber and also do not substantiallyincrease the effective surface area of the filter.

A number of different approaches have been taken to increase theeffective filtering surface area of a face mask; see, for example, U.S.Pat. Nos. 4,883,547 and 4,827,924, and EP-A 0,469,498 A2. EP-A 0,469,498A2, in particular, discloses a particle-filtering half mask that has afolded filter layer disposed between exterior and interior cover layers.The folded filtering layer is made of a porous, flexible filteringmaterial that is folded in an overlapping arrangement. A holding stripextending transverse to the fold direction is glued to the folds toensure that they lie flat. Other than indicating that the filter layermay be a multi-layer fiber fleece, EP-A 0,469,498 A2 does not disclosethe composition of the filtering material. Nor does the documentdisclose how the filtering layer is placed in a folded condition, and nodisclosure is made in regard to preserving the loft of the filteringmaterial during the manufacture of the folded filter.

Thermal Insulation

Nonwoven webs that contain polymeric microfiber are known to be usefulas thermal insulation. U.S. Pat. No. 4,118,531 to Hauser discloses anonwoven web that contains polymeric microfiber intermixed with crimpedstaple fiber. This nonwoven web demonstrates very good thermalresistance but lacks sufficient integrity to allow the web to beadhesively bonded to another surface and to allow the web to maintain acohesive structure after being subjected to abrasion. Used as insulationfor footwear and gloves and other apparel, the nonwoven web can beexposed to abrasion that can cause the web to be released from thesurface to which it is adhered and also may cause the web to losestructure and form clumps in the apparel. To overcome these problems,the nonwoven web may be embossed. Embossing, however, compresses the weband reduces its loft and therefor lowers its thermal resistance. Toraise the overall thermal resistance, more layers of embossed web mustbe employed, having the undesirable result of increasing the weight andcost of the apparel.

Corrugating Apparatus

Legions of corrugating apparatuses have been disclosed in the pastcentury. The corrugating apparatus art is replete with devices thatemploy mating gears to corrugate a flat web; see, for example, U.S. Pat.Nos. 4,116,603, 3,998,140, 3,905,857, 3,792,952, 3,723,213, 3,157,551,3,025,963, 2,051,025 and 1,290,800. Reciprocating corrugating devicesalso are well known in the corrugating apparatus art; see, for example,U.S. Pat. Nos. 4,650,102, 4,239,201, and 1,822,509. More recently, inU.S. Pat. No. 4,874,457 a corrugating apparatus has been disclosed whichcorrugates a flat web by (i) introducing the flat web onto the ends ofradially-extending paddles and then (ii) moving the ends of theradially-extending paddles towards each other to cause the web tocorrugate. The paddles move about a path that has a curved portion and astraight portion, and the apparatus corrugates the flat web when thepaddles move from the curved portion of the path to the straightportion. The web is maintained in a corrugated condition by passing theweb under an oven to bond adjacent folds of the corrugated web together.An optional cover layer can be introduced onto the tops of thecorrugations and also is passed under the oven to fuse the cover layerto the corrugations to stabilize the corrugated web.

SUMMARY OF THE INVENTION

The present invention provides a composite structure that comprises acorrugated, nonwoven web of polymeric microfiber (NWPM) and a means forretaining the shape of the corrugated NWPM. The corrugated NWPM has anaverage pore size of less than 150 μm, a solidity of 0.1 or less, and aplurality of generally parallel corrugations. The shape-retaining meansextends across the generally parallel corrugations and is secured to thecorrugated NWPM at valleys of the generally parallel corrugations suchthat the shape-retaining means is not coextensive with the corrugatedNWPM between two adjacent valleys.

In another aspect, the present invention provides a face mask thatcomprises a composite structure that is formed to fit over the nose andmouth of a person. The composite structure includes a corrugated NWPMthat has a solidity of 0.1 or less and a means for retaining thecorrugated shape of the corrugated NWPM. The shape-retaining means issecured to the corrugated at the valleys of the corrugations such thatthe shape-retaining means is not coextensive with the corrugated NWPMbetween two adjacent valleys.

In a further aspect, the present invention provides a filter capable ofremoving particulate and gaseous contaminants from the air. The filtercomprises first and second filter elements secured to each other andhaving a shape adapted for attachment to a respirator. The first filterelement comprises a corrugated NWPM having a solidity of 0.1 or less forremoving particulate contaminants, and the second filter elementcomprises a sorbent material for removing gaseous contaminants. A meansfor retaining the corrugated shape of the NWPM is secured to thecorrugated NWPM at valleys of the corrugations.

In a still further aspect, the present invention provides thermalinsulation that comprises a corrugated nonwoven web and a means forretaining the shape of the corrugated nonwoven web. The corrugatednonwoven web has a solidity of 0.1 or less and contains a mixture ofmicrofiber and crimped staple fibers that have a percent crimp of atleast fifteen percent. The shape-retaining means being secured tovalleys of the corrugations in the nonwoven web such that theshape-retaining means is not coextensive with the corrugated nonwovenweb.

In a still further aspect, the present invention provides a new methodof making a corrugated NWPM. The method comprises:

(a) introducing a NWPM having a solidity of 0.1 or less into acorrugating apparatus that has a plurality of paddles secured at a firstend to a means for moving the paddles about a path, the NWPM makingcontact with spaced second ends of the paddles opposite to the paddles'first ends; and

(b) reducing the spacing between the second ends of the paddles to causethe NWPM to become corrugated, wherein the corrugated nonwoven web ofpolymeric microfiber has a solidity of 0.1 or less.

In a still further aspect, the present invention provides a corrugatingapparatus that comprises:

(a) first and second paddles each attached at a first end to a means formoving the first and second paddles about a path, the first and secondpaddles extending radially from the moving means, and each paddle havinga second end for supporting a web as the first and second paddles moveabout the path, the second ends of the first and second paddles beingable to move towards each other to cause the web to corrugate; and

(b) an ultrasonic welding device located downstream to where the web iscorrugated, the ultrasonic welding device having a horn and an anvil,where the anvil includes the second ends of the first and secondpaddles, the ultrasonic welding device causing the corrugated web toform a bond with the shape-retaining means between the horn and theanvil where the corrugated web makes contact with the second edges ofthe first and second paddles.

A NWPM needs to be maintained in a lofty condition to obtain optimalfiltration performance. Filtration parameters such as pressure drop andservice life can be negatively impacted when a NWPM is compacted. A NWPMis delicate and thus care must be taken when handling such a web becauseit can be easily compacted and torn.

In this invention, a composite structure has been made that comprises alofty, corrugated NWPM. The lofty, corrugated NWPM has been madenotwithstanding the delicate nature of a NWPM. Using the method andapparatus of this invention, minimal contact is made with the NWPMthroughout the corrugation process to avoid compacting the web. Thisenables a corrugated NWPM to be made without sacrificing the web's loft.Web loft is measured by solidity, a parameter that defines the solidsfraction in a volume of web. Lower solidity values are indicative ofgreater web loft. A NWPM undergoes minimal changes in solidity whencorrugated using the method and apparatus of this invention to provide acorrugated NWPM, where the NWPM has solidity of less than 0.1. The NWPMis held in a corrugated condition by securing a shape-retaining means tothe valleys of the corrugations such that the shape-retaining means isnot coextensive with the corrugated NWPM. This composite structureprovides superior filtration performance over a flat NWPM, and thissuperior performance is demonstrated contemporaneously in threeimportant filtration parameters: particle penetration, pressure drop,and service life. A corrugated NWPM also can provide good thermalresistance. The performance parameters pertaining to filtration andinsulation incur no substantial detrimental effects when a NWPM iscorrugated in accordance with the present invention.

The above novel features and advantages of the invention are more fullyshown and described in the drawings and the following detaileddescription, where like reference numerals are used to represent similarparts. It is to be understood, however, that the drawings and detaileddescription are for the purposes of illustration only and should not beread in a manner that would unduly limit the scope of this invention.

GLOSSARY

In describing this invention:

The term "arithmetic median fiber diameter" means the fiber diameter forwhich equal numbers of fibers have diameters that lie above or belowthis value. The arithmetic median fiber diameter can be determinedthrough microscopic examination.

"Corrugated" means a surface that has peaks and valleys extending overthat surface;

"Corrugated surface area" (CSA) means the width of a corrugated webmultiplied by its length, where the length is taken along the corrugatedweb's "sinusoidal-type" path.

"Effective surface area" (ESA) means the area of a web available forfiltering. In a corrugated web, the ESA is equal to the CSA less theareas that are blinded off. By "blinded off" is meant those areas of webthat are rendered fluid inaccesible or fluid-impermeable. For example, aweb can become fluid impermeable where the shape-retaining means issecured (e.g., melt bonded, adhesive bonded, ultrasonically welded,etc.) to the corrugated web.

The term "microfiber" means fibers that have an arithmetic median fiberdiameter of less than 15 μm.

The term "pitch" means the center-to-center distance between the secondends of the paddles.

The term "nonwoven web of polymeric microfiber" (NWPM) means anentangled mass of fibers that has an arithmetic median fiber diameter ofless than 15 μm.

The term "solidity" means the volume of fibers per volume of web. It isa unitless fraction typically represented by α: ##EQU1## where m_(f) isthe fiber mass per sample surface area, which in the case of corrugatedwebs is the CSA; α_(f) is the fiber density; and L_(f) is the filterthickness, which in the case of corrugated NWPM is the NWPM thickness.Solidity is used herein to refer to the NWPM itself and not to thecomposite structure as a whole. When a NWPM contains mixtures of two ormore kinds of fibers, the individual solidities are determined for eachkind of fiber using the same L_(f), and these individual solidities areadded together to obtain the web's solidity, α.

The term "average pore size" (also known as average pore diameter) isrelated to the arithmetic median fiber diameter and web solidity and canbe determined by the following formula:

where D is the average pore size, d_(f) is arithmetic median fiberdiameter, and α is the web solidity. ##EQU2##

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a composite structure 10 in accordance with thisinvention.

FIG. 2 is a cross-section of composite structure 10 of FIG. 1 takenalong lines 2--2.

FIG. 3 is a front view of a face mask 22 in accordance with thisinvention.

FIG. 4 is a partial cross-section of a face mask body 23.

FIG. 5 is a perspective view of a filter 42 suitable for particulate andgaseous contaminant removal in accordance with this invention.

FIG. 6 is a partial cross-section of a filter 42 of FIG. 5 taken alonglines 6--6.

FIG. 7 is a side view of a corrugating apparatus 47 in accordance withthis invention.

FIG. 8 is an enlarged elevational fragmentary cross-section of acorrugating apparatus in accordance with this invention.

FIG. 9 is a front view of a paddle 48 in accordance with this invention.

FIG. 10 is a fragmentary side view of an alternative embodiment of acorrugating apparatus 47' in accordance with this invention.

FIG. 11 is a fragmentary side view of a further alternative embodimentof a corrugating apparatus 47'' in accordance with this invention.

FIG. 12 illustrates side views of the different composite structuresused in Examples 1-4 and C-1 to C-16.

FIG. 13 is plot of pressure drop as a function of time for sodiumchloride loading for the experiments of Examples 1-3 and C-1 to C-3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing the preferred embodiments of this invention, specificterminology will be used for the sake of clarity. The invention,however, is not intended to be limited to the specific terms soselected, and it is to be understood that each term so selected includesall the technical equivalents that operate similarly.

In FIGS. 1 and 2, there is illustrated an example of a compositestructure 10 according to this invention. Composite structure 10includes a corrugated NWPM 12. Corrugated NWPM 12 is secured to a means16 for retaining the corrugated shape of the NWPM 12 at the valleys 20of the NWPM 12. Although a valley 20 may become a "peak" by invertingNWPM 12, for purposes of simplicity, the term "valley" will be primarilythe only term used herein. As best shown in FIG. 2, the corrugated NWPM12 preferably follows an approximately sinusoidal-type curve when viewedfrom a side elevation. Adjacent sides 15 of adjacent corrugationspreferably do not overlap or make substantial contact with each other toa significant degree. Shape-retaining means 16 is not coextensive withcorrugated NWPM 12; that is, it does not follow the same approximatelysinusoidal-type path as the corrugated NWPM. As shown, shape-retainingmeans 16 can have a length substantially less than the length of thecorrugated NWPM 12 between two adjacent valleys 20. Shape-retainingmeans 16 preferably extends between two adjacent valleys as asubstantially straight line when viewed from a side elevation. Thestraight line distance between two adjacent valleys 20 is referred toherein as the "chord length" and is noted in FIG. 2 by the letter X.

The chord length, generally, is about 10 to 85 percent of the length ofthe corrugated NWPM between two adjacent valleys. The ratio of thelength of corrugated NWPM 12 to the chord length of the shape-retainingmeans may vary depending on the ultimate utility of the compositestructure but generally is about 10:1 to 1.2:1, and more typically 5:1to 1.5:1. This ratio is referred to as the corrugation ratio.

Corrugated NWPM 12 can be secured to shape-retaining means 16 bythermomechanical bonding (for example, ultrasonic welds), adhesivebonding (for example, hot melt bonding), mechanical means (for example,sewing), or other suitable means. The bond between corrugated NWPM 12and shape-retaining means 16 can extend along the whole length of avalley 20 when shape-retaining means 16 is a sheet or fabric 21. In apreferred embodiment, corrugated NWPM 12 is secured to shape-retainingmeans 16 by intermittent securement points 18, preferably ultrasonicwelds, located exclusively on valleys 20. Securement points 18 arepreferably spaced on each valley 20 by a distance Y (FIG. 1), and may beoffset from securement points 18 on an adjacent valley by a distance ofabout one-half Y. The value of Y can vary depending on, for example, thesize of securement points 18 and the size of corrugations 12. Ingeneral, however, Y is about 0.5 to 5 centimeters (cm).

By staggering the securement points on adjacent valleys 20, the numberof securement points 18 can be minimized per unit of exposed surfacearea of composite structure. This result is particularly beneficial whencomposite structure 10 is used as a filter because, in filteringapplications, it is desirable to have a maximum ESA. Minimizing the CSAused for securement helps maximize the ESA, and in so doing increasesthe service life of the filter and provides a lower pressure drop acrossthe filter or composite structure 10. Minimizing the CSA used forsecurement also may promote the thermal resistance of the compositestructure 10. A composite structure 10 of this invention can have lessthan 10 percent, preferably less than 5 percent, and more preferablyless than 2 percent of the CSA used for securement. In a more preferredembodiment, less than 0.5 percent of the CSA is used for securement.Further, it has been discovered that the use of intermittent securementpoints 18 does not substantially hamper the composite structure'sconformability or its use as a filter in a face mask.

Composite structure 10 can be conformed or bent around axis A thatextends parallel to the linear corrugations, as well as around axis Bthat extends transverse to the linear corrugations 12. Thisconformability permits the composite structure to be particularly usefulas a filter for a cup-shaped face mask or as thermal insulation in agarment or footwear. The degree of conformability may vary depending onthe particular shape-retaining means; however, if shape-retaining means16 is not particularly rigid, composite structure 10 may be bent aroundaxis A at a bend radius as small as about ten percent of the compositestructure thickness. Composite structure 10 may be bent around axis B ata bend radius as small as about the thickness of composite structure 10.For compound bending around axis A and B, the minimum bend radius isabout equal to the thickness of composite structure 10.

The particular composition and construction of the composite structure10 may vary with its intended utility.

The peak to valley height of a corrugated NWPM can vary but typically isabout 2 to 30 millimeters (mm), more typically 3 to 15 mm. For a facemask, the peak to valley height is about 4 to 8 mm. For thermalinsulation, the peak to valley height typically is about 4 to 50 mm,more typically about 10 to 25 mm.

The NWPM has an arithmetic median fiber diameter of less than about 15μm, preferably less than about 10 mm, and more preferably in the rangeof about 2 to 8 μm.

The NWPM, in general, has a basis weight in the range of about 25 to 100grams per square meter (g/m²) before being corrugated, and moretypically, the basis weight is in the range of 35 to 70 g/m².

The NWPM in corrugated form has a solidity of about 0.1 or less, morepreferably in the range of 0.04-0.08. For a face mask application, thesolidity of the corrugated NWPM preferably is in the range of about 0.05to 0.08. For thermal insulation, the solidity of a corrugated NWPMtypically is in the range of about 0.008 to 0.07.

The NWPM has an average pore size of less than about 150 μm and inpreferred embodiments the pore size is greater than 10 μm, morepreferably in the range of about 15 to 100 μm.

For filtration purposes, the NWPM preferably contains at least 50 weightpercent polymeric microfiber based on the weight of the fibrousmaterial. More preferably, the NWPM contains 80 weight percent polymericmicrofiber, and most preferably approximately one hundred 100 weightpercent polymeric microfiber based on the weight of fibrous material.The NWPM may contain fibers larger than microfibers such as largerdiameter staple fibers (see, U.S. Pat. No. 4,988,560 to Meyer et al.which discloses a web that contains polymeric microfiber and crimpedstaple fiber to provide a web of increased porosity).

The fibers of the NWPM are randomly entangled as a coherent mass offibers. The fibers can be entangled by, for example, a melt-blowingprocess, where a molten polymer is forced through a die and the extrudedfibers are attenuated by adjacent high velocity air streams to form anentangled mass of blown microfiber (BMF). BMF webs made in this mannerare held together by autogenous bonding. A process for making BMF websis disclosed in Wente, Van A., "Superfine Thermoplastic Fibers" 48Industrial Engineering Chemistry, 1342 et seq (1956); or see Report No.4364 of the Naval Research Laboratories, published May 25, 1954,entitled "Manufacture of Super Fine Organic Fibers" by Wente, Van A.;Boone, C. D.; and Fluharty, E. L. A NWPM that contains fibers other thanpolymeric microfibers such as crimped or uncrimped staple fibers may beprepared according to procedures discussed in U.S. Pat. No. 4,988,560 toMeyer et al., U.S. Pat. No. 4,118,531 to Hauser, and U.S. Pat. No.3,016,599 to Perry, the disclosures of which are incorporated here byreference. A NWPM may also be made using solution blown techniques suchas disclosed in U.S. Pat. No. 4,011,067 to Carey or electrostatictechniques such as disclosed in U.S. Pat. No. 4,069,026 to Simm et al.The fibers in a NWPM can be electrically charged to enhance theirfiltration capabilities; see U.S. Pat. No. 4,215,682 to Kubik et al. andU.S. Pat. No. 4,592,815 to Nakao.

Polymeric components that may be employed in a NWPM include polyolefinssuch as polyethylene, polypropylene, polybutylene,poly(4-methylpentene-1), and polyolefin copolymers; polyesters such aspolyethylene terephthalate (PET), polybutylene terephthalate, andpolyether ester copolymers such as HYTREL available from Dupont Co.,Elastomers Division, Wilmington, Del.; polycarbonates; polyurethanes;polystyrene; and thermoplastic elastomer block copolymers such asstyrene-butadiene-styrene, styrene-isoprene-styrene,styrene-ethylene/butylene-styrene, available from Shell Oil Company,Houston, Tex., under the trademark KRATON. Combinations of the abovepolymeric microfibers, or blends of the polymeric components, may alsobe employed. For example, a blend of polypropylene andpoly(4-methyl-1-pentene) can be used to make a NWPM (see U.S. Pat. No.4,874,399 to Reed et al.), or the NWPM may contain bicomponentmicrofiber such as the polypropylene/polyester fibers (see U.S. Pat. No.4,547,420 to Krueger et al.), the disclosures of these patents areincorporated here by reference. A corrugated NWPM 12 preferablycomprises fibers made from polyolefins, particularly fibers that containpolypropylene as a major fiber component (for example, greater thanninety weight percent) as such fibers can demonstrate good electricalcharge retention.

A NWPM may include other ingredients in addition to the fibrousmaterial. For instance, the NWPM may be loaded with discrete solidparticles capable of interacting with (for example, chemically orphysically reacting with) a fluid to which the particles are exposed.Typical particles for use in filtering or purifying include activatedcarbon, alumina, sodium bicarbonate, and silver particles. Suchparticles can remove a component from a fluid by sorption, chemicalreaction, or amalgamation or a catalyst may be employed to convert ahazardous gas to a harmless form. Examples of such particle-loadednonwoven webs of polymeric microfiber are disclosed in U.S. Pat. No.3,971,373 to Braun, where discreet solid particles are uniformlydispersed throughout and are physically held in a NWPM. The disclosureof this patent is incorporated here by reference. Also, additives suchas dyes, pigments, fillers, surfactants, abrasive particles, lightstabilizers, fire retardants, absorbents, medicaments, etc., may also beadded to a NWPM by introducing such components to the fiber-formingmolten polymers or by spraying them on the fibers after the NWPM hasbeen collected.

Although the corrugated NWPM illustrated in FIG. 2 has a single layer ofNWPM, this invention also contemplates corrugating a plurality of layersof NWPM to make a composite structure. A composite structure thereforecould comprise 2, 3, 4, etc. layers of corrugated NWPM, where eachadjacent layer is secured, ultimately, to the shape-retaining means toprovide a laminate of corrugated webs in the composite structure (see,for example, FIG. 12, sample b'). In a further embodiment, compositestructures of this invention may be stacked upon each other to provide aresulting composite structure that comprises a plurality of layeredcomposite structures (see, for example, FIG. 12, sample c').

Shape-retaining means 16 is an element capable of maintaining thecorrugated condition of a corrugated web. In a filtering application,shape-retaining means 16 allows composite structure 10 to be fluidpermeable in a direction normal to the extended surface of thecomposition structure and shape-retaining means 16 preferably does nothinder fluid flow through the composite structure 10 to a significantextent, and more preferably is not more restrictive to fluid flowthrough the composite structure 10 than the corrugated NWPM 12.Preferably, shape-retaining means 16 is sufficiently open or porous thatit demonstrates a pressure drop less than the pressure drop across thecorrugated NWPM 12. Also, shape-retaining means 16 preferably isdeformable, allowing composite structure 10 to be conformable.

Shape-retaining means 16 is illustrated in FIGS. 1 and 2 as a fabric 21of ultrasonically-bondable material that extends transverse and parallelto the parallel corrugations. Fabric 21 can be a porous and deformablenonwoven web such as a CELESTRA spun bond polypropylene fabric availablefrom Fiberweb North America Inc., Simpsonville, S.C., or the fabric 21may be a NWPM or other porous sheet-like materials including porouswoven webs. Alternatively, shape-retaining means 16 may take the form ofa plurality of spaced bands, filaments, or fibers extending across theparallel corrugations of NWPM 12, transverse to the parallelcorrugations or displaced diagonally to the same. Such bands, filaments,or fibers are bonded at the valleys of the corrugations to maintain thecorrugated shape of the NWPM 12. Examples of bands, filaments, or fibersthat could be employed include: thin bands having a pressure sensitiveadhesive applied thereto (for example, a thin tape); filaments coatedwith an adhesive; and polymeric fibers melt spun onto the valleys of thecorrugated NWPM while the melt spun fibers are in a tacky condition.When polymeric fibers are employed, they preferably have a compositionsimilar to the corrugated NWPM to permit melt bonding. A fabric 21 isthe preferred form of a shape-retaining means because it allows a lowerfrequency of bonding to the NWPM 12, thereby increasing the ESA of NWPM12.

In FIG. 3, an example of face mask 22 of this invention is illustrated.Face mask 22 has a mask body 23 that includes a corrugated filter layer25. Corrugated filter layer 25 provides a substantially expanded ESA anda high filter efficiency without substantially increasing the size ofthe face mask. A face mask of this invention can have an ESA of at least1.3 times the ESA of a face mask that is of substantially the same sizebut contains a non-corrugated filter layer. In general, the ESA can beincreased by a factor in the range of about 1.3 to 4, more typically 1.6to 2.5, without substantially increasing the size of the face mask.Thus, in accordance with this invention, a face mask can be providedwith an ESA exceeding about 200 cm², more preferably in the range ofabout 250 cm² to 600 cm².

As best shown in FIG. 4, a corrugated filter layer 25 can be acorrugated NWPM 12 held in a corrugated condition by a shape-retainingmeans 16 to form a composite structure 10 that is supported in a maskbody 23 by a shaping layer 24. Shaping layer 24 provides shape andstructure to the face mask and is porous to allow for relatively easypassage of air through the face mask. Shaping layer 24 can be located onthe interior of a face mask, and shape-retaining means 16 can bedisposed between shaping layer 24 and corrugated filter layer 25.Alternatively, corrugated filter layer 25 can be inverted so thatshape-retaining means 16 is located on the outer side of corrugatedfiltration layer 25, or corrugated filter layer 25 can be placed on theinner side of shaping layer 24 with the shape-retaining means locatedclosest to the face of the wearer. In the latter instance,shape-retaining means 16 preferably is made of a material that is softto the touch.

Corrugated filter layer 25 preferably is a NWPM that is in a loftycondition over substantially the whole surface of the corrugated NWPM. Acorrugated NWPM preferably has a solidity of 0.1 or less and does nothave tightly compacted corrugations to provide structure to the mask.Corrugated filter layer 25 can be secured to shaping layer 24 by, forexample, bonding corrugated filter layer 25 to a shaping layer 24 atmask base 26. The bond at mask base 26 may be formed by ultrasonicwelding, sewing, an adhesive such as a hot melt adhesive or pressuresensitive adhesive, encapsulation by a thermoplastic rubber, or thelike. Ultrasonic welds are the preferred means for bonding corrugatedfilter layer 25 to shaping layer 24 at mask base 26. Corrugated filterlayer 25 preferably is juxtaposed over substantially the whole surfaceof shaping layer 24.

Corrugated filter layer 25 preferably comprises about 1 to 4corrugations per cm of filter, more preferably 1.5 to 2.5 corrugationsper cm. There is about 8 to 20 mm of filter web between two adjacentvalleys. The ratio of the length of the filter web to the length ofshape-retaining means 16 between two adjacent valleys preferably isgreater than 1.5:1, more preferably in the range of 2.0:1 to 1.6:1.Corrugated filter layer 25 is preferably secured to shape-retainingmeans 16 by intermittent bonds, preferably ultrasonic welds, typicallyspaced at a distance Y (FIG. 1) of about 0.5 to 5 cm, more typically 1.5to 3 cm. The intermittent bonds each preferably occupy an area of lessthan 5 mm², and more preferably less than 2 mm². Corrugated filter layer25 can be assembled in a face mask as described in Example 22 of U.S.Pat. No. 4,807,619 to Dyrud et al., the disclosure of which isincorporated here by reference, by substituting the corrugated filterlayer 25 for the electrically-charged polypropylene BMF web. Thecorrugated filter layer is formed into a preformed filtration body thatis subsequently placed over an inner cup-shaped shaping layer and isbonded thereto.

A variety of materials may be used in a shaping layer. For example, ashaping layer may comprise a cup-shaped, open mesh plastic or metal or amolded nonwoven web of fibers. A face mask of this invention typicallyemploys a molded nonwoven web of fibers as a shaping layer. A nonwovenweb of fibers can be molded by including thermal bonding components inthe fibers, which allow the fibers to become bonded to one another atpoints of fiber intersection after being cooled. Such thermal bondingfibers are available in single component and bicomponent forms.Bicomponent fibers are the preferred thermal bonding fibers for formingshaping layers because they produce a more openly structured shapinglayer. Additionally, staple fibers in crimped or uncrimped form may alsobe incorporated into the shaping layer. Shaping layers of this kind arewell known in the art and have been described in InternationalApplication No. PCT/US91/08531, U.S. Pat. No. 4,536,440 to Berg, U.S.Pat. No. 4,807,619 to Dyrud et al., and U.S. Pat. No. 4,827,924 toJapuntich, the disclosures of which are incorporated here by reference.Although the term "shaping layer" is used in this description with theprimary purpose of providing shape to a face mask, a shaping layer canalso have other functions, which in the case of an outer shaping layermay even be a primary function, such as protection of the corrugatedfiltration layer and prefiltration of a gaseous stream, or the shapinglayer may serve as a means 16 for retaining the corrugated shape of thecorrugated filtration layer.

As shown in FIG. 3, a pliable dead-soft band 30 of metal such asaluminum can be provided on mask body 23 to allow it to be shaped tohold the face mask in a desired fitting relationship to the nose of thewearer. Mask body 23 can have an annular mask base 26 that makes a snugfit to the wearer's face by use of straps 28 or other suitable meanssuch as tie strings, an adjustable harness, and the like. Although thecup-shaped mask body 23 has a curved, hemispherical shape, the mask bodycan take on other shapes. For example, the mask body can be a cup-shapedmask having a construction like the face mask disclosed in U.S. Pat. No.4,827,924 to Japuntich.

In FIGS. 5 and 6, an example of a filter 42 for use in a respirator (notshown) is illustrated. Filter 42 would be used in a respirator that hasa fluid-impermeable mask body molded to accommodate filter 42. Filter 42comprises first and second filter elements 43 and 44 for filteringparticulate and gaseous contaminants, respectively.

First filter element 43 removes particulates from the air and includes acorrugated NWPM 12. Corrugated NWPM 12 can be secured to ashape-retaining means 16 as described above to form a compositestructure 10. Composite structure 10 can be secured to an outer surfaceof rigid body 46 to act as a prefilter that filters out particulates toprevent them from entering filter element 43.

Second filter element 44 comprises a sorbent filter material forremoving gaseous contaminants. The sorbent material may be in the formof a plurality of sorbent granules 45 united in the form of a rigid body46 such as described in U.S. Pat. No. 5,033,465 to Braun, the disclosureof which is incorporated here by reference. Such a bonded sorbentstructure includes sorbent granules 45 bonded together by polymericbinder particles to form rigid body 46. Rigid body 46 preferably is aunified impact-resistant structure. The sorbent granules are uniformlydistributed throughout the rigid body and are spaced to permit a fluidto flow therethrough. The sorbent granules can be, for example,activated carbon granules, and the polymeric binder particles can be,for example, polyurethane, ethylene-vinyl acetate, and polyethylene. Alayer 51 of nonwoven fiber can be secured to the surface of rigid body46 opposite composite structure 10 to protect the sorbent particles fromabrasion. Second filter element 44 may also comprise a plurality ofloose or unbonded sorbent granules placed together in a container towhich the second filter element is secured.

Although the composite structure 10 of the invention has beenillustrated as being useful as a filter element, the composite structure10 also can be used as thermal insulation. In such an instance, thecorrugated NWPM preferably contains crimped staple fiber as taught inU.S. Pat. No. 4,118,531 to Hauser. Crimped staple fibers have acontinuous wavy, curly, or jagged character along their length andaverage about 2 to 15 centimeters in length with a crimp count of atleast about 2 crimps per centimeter. The crimped staple fibers generallyare larger diameter fibers which are randomly and thoroughly intermixedand intertangled with the microfiber and account for approximately atleast ten weight percent, and preferably in the range of about 25 to 75weight percent of the fibers in the web. The staple fibers typicallyhave a percent crimp of at least about fifteen percent, and preferablyat least about 25 percent. The webs disclosed in Hauser provide verygood thermal insulating efficiency per unit weight and after having beencorrugated and united to a shape-retaining means provide a compositestructure having good integrity and thermal resistance, making compositestructures which utilize such webs valuable insulators for apparel suchas jackets, coats, and footwear, including boots, and also for otherarticles such as sleeping bags. The composite structures may be securedto such articles by adhesive bonding, stitching, gluing, and the like.

Turning to FIG. 7, an example of corrugating apparatus 47 of thisinvention is shown which is useful for continuously making a compositestructure according to the method of this invention. The apparatusillustrated in FIG. 7 is particularly advantageous for making acorrugated NWPM. Using the method and apparatus of this invention, alofty NWPM can be corrugated without tearing the web or substantiallyincreasing its solidity. NWPM are delicate: they can be easily torn andcompacted, which conditions can render the NWPM unsuitable for use in aface mask. Torn webs allow contaminants to pass through the face mask,and compacted webs can cause significant increases in pressure drop.Good web loft also is important for thermal insulation. Face masks thathave high pressure drops can be very uncomfortable to wear. Inaccordance with this invention, corrugated NWPM webs can be made withoutincreasing the starting web's solidity by more than 15 percent onaverage, more preferably by not more than 3 to 5 percent on average. Inmany embodiments, the solidity of the NWPM is increased by not more thanone percent or is so insignificant to be unnoticeable. There is verylittle contact with the web using the method and apparatus of thisinvention, and thus the loft or thickness of the web and ultimately thesolidity is preserved and lower pressure drops are obtained. Further,the method of retaining the corrugated pattern of the corrugated webprovides a maximum ESA on the resulting product.

Corrugating apparatus 47 has a plurality of paddles 48 attached at afirst end 49 to a means 50 for moving the paddles about an endless path52. Each paddle 48 has a second end 54 for supporting a web 56 or 66 (56designates the starting material or non-corrugated web, and 66designates the corrugated web) as the paddles move about path 52. Path52 has a curved portion 53 and a straight portion 55. The second ends 54of the paddles are able to move toward each other (that is, pitchdecreases) as the curved portion 53 approaches the straight portion 55at region 58 of path 52 to cause web 56 to corrugate.

Means 50 preferably is a single flexible belt 57 (FIG. 8), but may alsobe, for example, a plurality of spaced parallel flexible belts. By"flexible" is meant the belt can be bent or deflected orthogonal to themachine direction so that the belt can assume a 360 degree path. Whenthe paddle moving means 50 is flexible belt 57, paddles 48 can beembedded in flexible belt 57 at their first end 49 at spaced intervals.The paddles' first ends are preferably embedded in the belt such thatthe edge of the first end 49 is approximately flush with the innersurface of flexible belt 57. Preferably, at least 70 percent, morepreferably at least 85 percent, of the total paddle length extends fromthe belt 57. Belt 57 preferably is about 5 to 15 mm thick, morepreferably 7 to 10 mm thick.

The paddles move in the machine direction with the belt and areconstrained to remain normal to a tangent of the flexible belt 57. Thespacing of the paddles defines chord length, and so it is important thatthe paddles' first ends do not move or vibrate laterally in the machinedirection. Flexible belt 57 preferably is made from a material thatstabilizes the paddles' position so that the chord length in theresulting corrugated web 66 can be kept consistent. A rubber belt havinga Shore A durometer in the range of 25 to 90 can be suitable forstabilizing the paddles' position It has been discovered that a rubberbelt made from silicone rubber can adequately constrain the paddles toprevent lateral movement. Examples of suitable silicone rubbers includeRTV-630 available from General Electric, and Silastic Type L RTV used inconjunction with a Type E curing agent, both available from Dow Corning.

As shown in FIG. 8, belt 57 can be further supported by running aplurality of parallel reinforcing members 59 through the belt 57.Parallel reinforcing members 59 are embedded in belt 57 and can be anysuitable chord, line, strand, etc. that would not break or undulystretch under normal operating conditions. As shown in FIG. 9, first end49 of the paddles 48 can have a plurality of openings 61 to accommodatethe parallel reinforcing members 59. Parallel reinforcing members passthrough openings 61 throughout belt 57 to assist in the securement ofpaddles 48 to belt 57. First end 49 of a paddle 48 can also be providedwith an irregular configuration including baffles or other openings 63that promote constrainment of paddles 48 in belt 57.

Corrugating apparatus 47 has a first means 60 for introducing anon-corrugated web 56 to corrugating apparatus 47. First means 60 causesnon-corrugated web 56 to make contact with the paddles' second ends 54upstream to where the non-corrugated web 56 is corrugated at 58. Asecond means 64 is provided for introducing a means 16 for retaining thecorrugated shape of the corrugated web 66. The second means 64 causesthe shape-retaining means 16 to make contact with corrugated web 66downstream to where it is corrugated at 58. A means 70 secures theshape-retaining means 16 to corrugated web 66.

First means 60 for introducing a non-corrugated web 56 to apparatus 47can include a stationary guiding member 72. Guiding member 72 preferablyhas a flared end 73 and a curvature that corresponds to the arc createdby the second ends 54 of paddles 48 as they move about path 52 on curvedportion 53. Guiding member 72 causes non-corrugated web 56 to makecontact with the paddles' second ends 54 on the curved portion 53 ofpath 52. Non-corrugated web 56 will typically feed off a roll orextruder (not shown).

Guiding member 72 can also extend over the straight portion 55 of path52 to preserve the corrugated condition of web 66. In such a location,member 72 retains the web 66 relative to the paddles' second ends 54 asthe paddles 48 move about path 52. A weight 74 or other suitable meanscan be placed on member 72 to maintain a slight degree of pressure onweb 66 at the paddles' second ends 54. In lieu of guiding member 72 topreserve the web's corrugated condition, other means such as airimpingement or a circulating contact belt may be employed.

Second means 64 for introducing a shape-retaining means to corrugatedweb 66 can include, for example, a bobbin 76 that turns to feed ashape-retaining means 16 such as a porous nonwoven sheet (or a pluralityof linear bands, filaments, or fibers) that is to be fastened to thecorrugated web 66. Shape-retaining means 16 can make contact withcorrugated web 66 by using a guiding member with a flared end similar to73, or as shown in FIG. 7, shape-retaining means 16 can be placed incontact with corrugated web 66 by passing means 16 under securing means70.

Securing means 70 is a device that attaches corrugated web 66 toshape-retaining means 16. Securing means 70 may be, for example, athermomechanical bonding apparatus, a melt spinneret system, a pressureroller, and the like. Securing means 70 preferably secures corrugatedweb 66 to shape-retaining means 16 selectively at valleys 20 of thecorrugations. To make a composite structure for a filtering face mask,securing means 70 preferably attaches a corrugated NWPM to ashape-retaining means 16 in a manner that least disturbs the loftycondition of the corrugated nonwoven web.

A preferred securing means 70 for use with a NWPM is a thermomechanicalbonding apparatus. A thermomechanical bonding apparatus, such as anultrasonic welding device, can selectively secure a corrugated web to ashape-retaining means in a manner which least disturbs the loftycondition of a corrugated NWPM, thereby preserving the web's utility asa filter. An ultrasonic welding device has a horn 78 driven by astandard commercially available ultrasonic power device (not shown). Theanvil includes paddles 48, and the paddles' second ends 54 act as anvilcontact surfaces. Ultrasonic vibrations in horn 78 cause a corrugatedweb 66 to be melt bonded to the shape-retaining means 16 over the secondends 54 of paddles 48. A supporting member 79 such as a roller ispreferably located opposite horn 78 adjacent to paddles' first ends 49.Supporting member 79 assures that web 66 and shape-retaining means 16absorb the ultrasonic signals to form a bond therebetween, as opposed toallowing paddles 48 to vibrate. The ultrasonic vibrations from horn 78are preferably concentrated at discreet regions over paddles' second end54 to form intermittent securement points 18, as shown in FIGS. 1 and 2.

In FIG. 9, a front view of a paddle 48 is shown. Paddle 48 has aplurality of spaced energy concentrators 62 in the form of spacedprotrusions on the paddles' second end 54. Energy concentrators 62 causecorrugated web 66 to be bonded to shape-retaining means 16 above eachenergy concentrator. To make a composite structure 10 that has thestaggered spot welds illustrated in FIGS. 1 and 2, the second ends 54 ofa paddle is provided with spaced energy concentrators 62 that are offsetfrom the energy concentrators of an adjacent paddle, for example, atapproximately one-fourth to one-half the distance between concentratorson adjacent paddles, more preferably at about one-half the distance (seeY FIG. 1). Alternatively, the energy concentrators may be randomlyspaced on each paddle. The size of the energy concentrators may varydepending on the number of web layers and the size of the corrugationsin the corrugated web, but typically have a top surface area of about 1to 10 mm², more typically 2 to 6 mm². To form a corrugated filtrationlayer for a face mask, the top surface area of the energy concentratorsis about 2 to 4 mm². In general, the paddles 48 are about 1 to 2 mmthick, and more typically about 1 to 1.5 mm thick.

As shown in FIG. 7, it is possible to contemporaneously corrugate morethan one web 56. A plurality of non-corrugated webs 56 (dotted lines)can be fed into the corrugating apparatus 47 simultaneously at 60. Whenso doing, each web 56 becomes corrugated at the same time as thepaddles' second ends 54 move towards each other at 58. Ultrasonic weldsor other bonding means can secure corrugated web 66 to a shape-retainingmeans 16 to provide a coextensive laminate of corrugated webs 66 in theresulting composite structure.

The apparatus of this invention also allows composite structures to bemade which have various amounts of corrugated web 66 per a given chordlength. The amount or length of the web between two adjacent peaks orvalleys 20 is determined by the pitch of the paddles at the point of webintroduction. To explain the effect of pitch by way of example, consideradjacent paddles 48 having second ends 54 spaced 1 cm (pitch=1 cm) whereweb 56 first makes contact with the paddles' second ends 54 on curvedportion 53. With the paddles spaced as such, there would be 1 cm ofcorrugated web 66 between two adjacent peaks or valleys 20 in theresulting composite structure 10. The pitch of the paddles where bondingoccurs on straight portion 55 determines the chord length for eachindividual corrugations. If the paddles have a pitch of 0.5 cm at thepoint of securement, the chord length will be 0.5 cm between adjacentvalleys on the resulting composite structure to provide a corrugationratio of 2:1.

Turning to FIG. 10, an alternative embodiment of a corrugating apparatus47' is shown. In corrugating apparatus 47' the paddles 48' move about apath 52' that has a curved portion 53' that has a varying bend radius.The varying bend radius causes adjacent second ends 54' to have adecreasing pitch in the direction of paddle movement. This decrease inpitch, in turn, causes web 56' travelling on paddles' second ends 54' tobe corrugated. The bend radius in apparatus 47' increases as the paddles48' move downstream along the curved portion 53'.

Corrugating apparatus 47' has a first means 60' for introducingnon-corrugated web 56' to the paddles' second ends 54'. First means 60'preferably has a plurality of locations for introducing non-corrugatedweb 56' on the curved portion of path 52'. FIG. 10 illustrates fivedifferent locations where non-corrugated web 56' can be introduced toapparatus 47'. At location 1, the paddles' second ends 54' are moving atthe fastest speed (pitch is the greatest here) and therefore morenon-corrugated web 56' will be introduced to the apparatus 47' at thatlocation. This will result in a corrugated web 66' having a greateramount of corrugated web per chord length than, for example, a webintroduced at locations 2, 3, 4, or 5. A web 56' introduced at location5 would have the least amount of corrugated web 66' per chord length onthe resulting composite structure. Therefore, by changing the point ofweb introduction, the corrugation ratio can be altered when usingapparatus 47'.

Belt 57' can be supported over the curved portion 53' of path 52' on amodule 80'. Module 80' carries a plurality of movable members such asrollers or balls 82'. Balls 82' rotate and circulate through the module80' as belt 57' moves about the curved portion 53' of path 52'. When theballs 82' reach the end of the curved portion 53' of path 52', the balls82' drop to the bottom of module 80' to be recirculated again. Module80' can be fashioned so that it can be quickly removed and replaced witha module having a different varying bend radius. Thus, as an alternativeto introducing the web at various locations along a curve with a varyingbend radius, different corrugation ratios may be obtained by holding thepoint of web introduction constant and varying the bend radius byinserting a module of a different bend radius.

In FIG. 11, a further alternative embodiment of a corrugating apparatus47'' is shown. Corrugating apparatus 47'' has a means 88'' for alteringthe pitch of paddles' second ends 54''. Pitch altering means 88'' islocated along the path 52'' adjacent to the means 70'' for securing theshape-retaining means 16'' to the nonwoven corrugated web 66''. Thepitch altering means 88'' operates by deflecting the paddle moving means50'' in a direction orthogonal to the machine direction (as shown by thevertical double arrow). This deflection occurs where the shape-retainingmeans 16'' is bonded to corrugated web 66''. An ultrasonic weldingdevice can be employed in this embodiment to bond corrugated web 66'' toa sheet of ultrasonically-bondable fabric or other means such as aplurality of bands, filaments, threads, or fibers. By decreasing thepitch here, there is a decrease in chord length and therefore anincrease in the number of corrugations per unit length of the resultingcomposite structure. To avoid tearing web 66'', it is important that thebend radius at 90'' is not less than the bend radius at the point of webintroduction. It is also important to remove the composite structure10'' from the paddles' second ends 54'' before they move apart at bend92''; otherwise, the composite structure 10'' can be damaged. AlthoughFIG. 11 illustrates path 50'' being deflected in a manner that causeschord length to decrease, path 50'' also could be deflected in theopposite direction to increase chord length.

Other features and advantages of this invention are further illustratedin the following examples. It is to be expressly understood, however,that while the examples serve this purpose, the particular ingredientsand amounts used as well as other conditions and details are not to beconstrued in a manner that would unduly limit the scope of thisinvention.

EXAMPLES

Nonwoven Web of Polymeric Microfiber

The NWPM used in the following examples was an electrically-chargedpolypropylene BMF web that had an average basis weight of 55 grams persquare meter (g/m²), an average thickness of 0.086 cm (0.034 inch) (asmeasured while applying a 0.1 g/cm² force using a Low Pressure ThicknessGauge Model No. CS-49-46 available from Custom Scientific Instruments,Inc., Whippany, N.J.), a fiber density π_(f) of 0.91, and a solidity ofless than approximately 0.08.

Shape Retaining Means

The shape retaining means used in the following examples was a 16.95g/m² (0.5 oz./sq. yd.) CELESTRA nonwoven spunbond polypropylene fabricavailable from Fiberweb North America, Inc., Simpsonville, S.C.

Web Corrugation

The corrugating apparatus used to fabricate corrugated NWPM in thefollowing examples was similar to the corrugating apparatus shown inFIG. 7. The apparatus had a flexible endless belt 27.9 cm in width and0.64 cm thick (0.25 inch) and was made from silicone rubber (RTV-630,available from General Electric). Steel paddles were embedded at a firstend in the rubber belt such that the edge of the first end was flushwith the inside surface of the belt. Nylon chords 1.5 mm (0.06 inch) indiameter (surveyor's snap line) ran through openings 61 (FIG. 9) in theends of the paddles for reinforcement. The paddles were 0.12 cm (0.047inch) thick, were 3.18 cm (1.25 inch) high, and were 27.9 cm (11 inches)wide at the embedded first end and 24.1 cm (9.5 inch) wide at the secondfree end. The paddles embedded ends were spaced center-to-center at 0.64cm (0.25 inch) as measured on the straight portion of the path. Aplurality of spaced energy concentrators were located along the upperedge of the paddles as illustrated in FIG. 9. The concentrators were0.318 cm (0.125 inch) wide, extended 0.102 cm (0.040 inch) above thepaddle edge, and were spaced center-to-center at 3.18 cm (1.25 inch).The concentrators on adjacent paddles were offset by 1.59 cm (0.63inch). The belt traveled over 6.35 cm (2.5 inch) diameter rollers spacedaxis-to-axis at approximately 20 cm (7.875 inches), creating twostraight portions on the path of the same length. The flexible beltassembly was driven by a variable speed gear motor.

The corrugation apparatus was equipped with a BRANSON 501 ultrasonicwelder assembly with a 2.5:1 booster driving a 17.78 cm (7 inch) widehorn having a 2.54 cm (1 inch) thick face. The welder was driven by aBRANSON 1300P power supply controlled by a variac. The leading andtrailing edge of the horn had a slight curvature to facilitate passageof the NWPM and CELESTRA fabric under the horn. The force on the webbetween the face of the ultrasonic horn and the paddle energyconcentrators was regulated by an air pressure cylinder so as tominimize damage to the NWPM.

Using the above-described corrugating apparatus, the resultantcorrugated webs had an approximate corrugation ratio of 1.7:1 and thesecurement points rendered approximately 1.1% of the CSA unavailable forfiltering.

During the corrugation process, three parameters were controlled toinsure sufficient securement of the NWPM to the CELESTRA fabric withoutcreating holes in the NWPM by "over-welding" or "over-pressure". Thesethree parameters were: 1) the force applied to the NWPM and CELESTRAfabric from the ultrasonic horn and the energy concentrators, 2) thepower supplied to the welding horn, and 3) the speed of the corrugatingbelt. Representative run conditions for producing the corrugated webconfigurations were as shown in Table 1:

                  TABLE 1                                                         ______________________________________                                                     Horn                                                                          Cylinder   Welder   Belt Speed                                                Pressure   Power    Meters Per                                   Web Configuration                                                                          (kg/cm.sup.2)                                                                            (Watts)* Minute (mpm)                                 ______________________________________                                        1 Layer NWPM and 1                                                                         0.56       1050     15.8                                         layer CELESTRA fabric                                                         2 Layers NWPM and 1                                                                        0.70       1200     13.4                                         layer CELESTRA fabric                                                         ______________________________________                                         *Estimated power based on power supplied to welder                       

The NWPM web and CELESTRA fabric were drawn into the corrugatingapparatus by the circulating paddle action and were welded together justabove the energy concentrators. After welding the NWPM and the CELESTRAfabric together, the resulting composite structure was removed from thepaddles before the free ends of the paddles began to spread at thecurved portion of the path.

The configuration of the composite structures that were used in theseExamples are shown in FIG. 12, where numeral 12 designates thecorrugated NWPM, numeral 14 designates the flat NWPM, and numeral 21represents the CELESTRA fabric. The flat composite structures are notedas structures a-c, and the composite structures that contain corrugatedNWPM are noted as structures a'-c'. Composite structures that contained2-layers of corrugated NWPM (structure b') were prepared by feeding twoflat webs from their respective rolls into the corrugating apparatus inan unbonded, face-to-face configuration. The 3-layer corrugated web(structure c') was prepared from two separate composite structures,namely, a 1-layer corrugated NWPM bonded to a CELESTRA fabric (structurea') and a 2-layer corrugated NWPM bonded to a CELESTRA fabric (structureb'). In this three layer configuration, the individual compositestructures were placed in back-to-face contact without being attached toeach other.

Pressure Drop and Particle Penetration Testing

Comparative performance of the various filter examples was determinedusing a method similar to Military Standard MIL-STD-282, wherein thefilter configurations were subjected to particulate challenges and theparticle concentrations upstream and downstream of the filter weremonitored. Testing was conducted on a Model 8110 Automatic Filter Tester(AFI), available from Thermo Systems, Inc., St. Paul, Minn. Eachcomposite structure was challenged with a solid (NaCl) and/or a liquid(dioctyl phthalate, (DOP)) aerosol which were generated from a 2% NaClsolution in distilled water or neat DOP, respectively at flow rates of85 liters per minute (lpm) as indicated. The NaCl aerosol had alog-normal distribution with a particle size count median diameter of0.10 micrometers and a geometric standard deviation of 1.9. The DOPaerosol had a log-normal distribution with a particle size count mediandiameter of 0.19 microns and a geometric standard deviation of 1.5.Aerosol concentration upstream and downstream of the filter wasmonitored by a photometer with filter penetration calculated by amicroprocessor. Testing is automatic with the data for pressure drop,penetration, flow rate, and particulate challenge displayed and loggedon an auxiliary computer.

Using the pressure drop and penetration data, a quality factor, Q, canbe calculated. The Q factor is a unitless property that measures afilter's performance at a given flow rate for a given filterconfiguration. ##EQU3## The formula for calculating the Q factor islinear relative to the pressure drop, and is exponential relative to thepenetration. In a comparison of Q factors by means of a linear analysis,a larger positive Q factor value indicates better filter performance indirect linear proportion.

Examples 1-3 and Comparative Examples C-1 to C-3

All samples tested were circular samples, 13.3 cm (5.25 inches) indiameter that were cut from composite structures having theconfigurations shown in FIG. 12. The samples were mounted in a sampleholder which exposed a circular (diameter of 11.22 cm (4.42 inch))portion of the sample to the particulate challenge. Flat NWPM samplesillustrated in FIG. 12 as composite structures a-c had an ESA of 99 cm²and composite structures a'-c' occupied the same surface area in thesample holder but had a corrugation ratio of 1.7:1 to provide a greatlyexpanded ESA.

In each example, five (5) samples were tested for the initialpenetration and initial pressure drop and the results of these testswere averaged and are reported in Tables 2 and 3. A quality factor, Q,was calculated from the averaged penetration and pressure drop data.

                  TABLE 2                                                         ______________________________________                                        DOP Challenge                                                                                 Initial                                                                       Pressure Initial        Q Factor                                              Drop     Penetration                                                                           Quality                                                                              Ratio                                 Example                                                                              Structure                                                                              (mmH.sub.2 O)                                                                          (percent)                                                                             Factor Q                                                                             Corr/Flat                             ______________________________________                                        C-1    a        4.98     29.800  0.24                                         C-2    b        11.34    6.564   0.24                                         C-3    c        17.32    1.744   0.23                                         1      a'       3.34     24.720  0.42                                         2      b'       8.72     3.824   0.37                                         3      c'       12.12    1.029   0.38   1.63                                  ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        NaCl Challenge                                                                                Initial                                                                       Pressure Initial        Q Factor                                              Drop     Penetration                                                                           Quality                                                                              Ratio                                 Example                                                                              Structure                                                                              (mmH.sub.2 O)                                                                          (percent)                                                                             Factor Q                                                                             Corr/Flat                             ______________________________________                                        C-1    a        5.10     7.585   0.51                                         C-2    b        11.33    0.520   0.46                                         C-3    c        16.76    0.075   0.43                                         1      a'       3.58     5.755   0.80                                         2      b'       8.76     0.260   0.68                                         3      c'       13.36    0.023   0.63   1.50                                  ______________________________________                                    

The data in Tables 2 and 3 illustrates the superior performance of thecomposite structures of this invention. In Examples 1-3, the corrugatedconfigurations a'-c' of this invention provided lower pressure drops,lower penetration values, and larger Q factors as compared to thenon-corrugated composite structures a-c of comparative examples C-1 toC-3, respectively.

The average Q factors for a DOP challenge aerosol are 0.39 for compositestructures a'-c' of Examples 1-3 and are 0.24 for composite structuresa-c of Comparative Examples C-1 through C-3. The ratio of these twoaveraged Q factors (Q corrugated/Q flat) is 1.63. Similarly, the averageQ factors for NaCl are 0.70 for composite structures a'-c' of Examples1-3 and are 0.47 for composite structures a-c of Comparative ExamplesC-1 through C-3. These two averaged Q factors give a ratio (Qcorrugated/Q flat) of 1.50. The 1.63 and 1.50 ratios demonstrate thatthis invention provides a Q factor improvement in performance of 63% and50%, respectively.

Service Life Testing

Composite structures a-c and a'-c' shown in FIG. 12 were tested forservice life by measuring pressure drop and penetration while exposed toa particulate challenge over certain periods of time. The particlechallenge was sodium chloride. Pressure drop and particle penetrationwere sampled every minute over a time span of at least twenty-fiveminutes. Each structure (a-c and a'-c') was tested in five separatetrials. The data for the five separate trials was averaged and theaveraged pressure drop, penetration, and Q factor data is reported inTable 4, where pressure drop is abbreviated as ΔP, and penetration isabbreviated as "Pen.".

                                      TABLE 4                                     __________________________________________________________________________    Service Life Tests for Flat Composite Structures of this Invention                      Approximate Elapsed Time (minutes)                                  Example                                                                            Structure   1   5   10  15  20  25                                       __________________________________________________________________________    C-1  a    ΔP (H.sub.2 O)                                                                 5.17                                                                              9.47                                                                              16.33                                                                             33.83                                                                             83.80                                                                             157.83                                             Pen. (%)                                                                             8.583                                                                             3.270                                                                             1.517                                                                             0.231                                                                             0.005                                                                             0.001                                              Q Factor                                                                             0.48                                                                              0.36                                                                              0.26                                                                              0.18                                                                              0.12                                                                              0.07                                     C-2  b    ΔP (H.sub.2 O)                                                                 11.93                                                                             16.83                                                                             24.60                                                                             46.10                                                                             103.50                                                                            181.50                                             Pen. (%)                                                                             0.769                                                                             0.220                                                                             0.103                                                                             0.013                                                                             0.001                                                                             0.001                                              Q Factor                                                                             0.41                                                                              0.36                                                                              0.29                                                                              0.19                                                                              0.11                                                                              0.06                                     C-3  c    ΔP (H.sub.2 O)                                                                 18.93                                                                             24.27                                                                             32.20                                                                             55.80                                                                             118.63                                                                            207.50                                             Pen. (%)                                                                             0.078                                                                             0.024                                                                             0.011                                                                             0.001                                                                             0.001                                                                             0.001                                              Q Factor                                                                             0.38                                                                              0.34                                                                              0.28                                                                              0.21                                                                              0.10                                                                              0.06                                               Avg. Q Factor                                                                        0.42                                                                              0.36                                                                              0.27                                                                              0.19                                                                              0.11                                                                              0.06                                     1    a'   ΔP (H.sub.2 O)                                                                 4.10                                                                              6.37                                                                              9.27                                                                              13.30                                                                             20.03                                                                             32.83                                              Pen. (%)                                                                             5.880                                                                             2.167                                                                             1.587                                                                             0.870                                                                             0.322                                                                             0.072                                              Q Factor                                                                             0.69                                                                              0.57                                                                              0.45                                                                              0.36                                                                              0.29                                                                              0.22                                     2    b'   ΔP (H.sub.2 O)                                                                 9.37                                                                              11.80                                                                             14.66                                                                             18.70                                                                             25.20                                                                             36.93                                              Pen. (%)                                                                             0.274                                                                             0.111                                                                             0.070                                                                             0.041                                                                             0.017                                                                             0.005                                              Q Factor                                                                             0.63                                                                              0.58                                                                              0.49                                                                              0.42                                                                              0.35                                                                              0.27                                     3    c'   ΔP (H.sub.2 O)                                                                 13.60                                                                             16.10                                                                             19.00                                                                             23.00                                                                             29.63                                                                             45.56                                              Pen. (%)                                                                             0.040                                                                             0.017                                                                             0.011                                                                             0.006                                                                             0.002                                                                             0.001                                              Q Factor                                                                             0.38                                                                              0.58                                                                              0.54                                                                              0.48                                                                              0.42                                                                              0.27                                               Avg. Q Factor                                                                        0.63                                                                              0.56                                                                              0.47                                                                              0.40                                                                              0.33                                                                              0.25                                     Average Q Factor Ratio (Corr./Flat)                                                            1.50                                                                              1.58                                                                              1.74                                                                              2.07                                                                              3.08                                                                              3.96                                     __________________________________________________________________________

The data set forth in Table 4 demonstrates that, as the sodium chlorideparticulates were deposited on the corrugated and flat compositestructures, the pressure drop for the flat composite structures (a-c)increased significantly, whereas the composite structures that containcorrugated NWPM (a'-c') do not demonstrate such significant pressuredrop increases. FIG. 13 shows the superior pressure drop values that areobtained by the composite structures of the invention, where pressuredrop is plotted as a function of time. The flat NWPM configurations(a-c) show a significant change in the slope of the plot atapproximately 12 minutes; whereas the composite structures that containcorrugated NWPM (a'-c') showed very little increase in pressure drop upto 25 minutes, and the change in slope for the corrugated NWPM (a'-c')is much less than that of the flat composite structures (a-c).

A comparison of the average Q factors for the corrugated and flat webcomposite structures at the indicated time intervals shows that at theone minute interval, the ratio is 1.50 which is identical to the ratioset forth in Table 3 for the NaCl initial exposure. As the elapsed timeincreases, however, the ratio of Q factors (Q corrugated/Q flat)increases to almost 4 at 25 minutes, thus demonstrating a largemagnitude of better performance with this invention.

Web Thickness Testing and Solidity Determination

The impact of the corrugating apparatus and method of this invention onweb thickness was tested. Solidity is a function of web thickness, andthus to provide a web of low solidity, it is important to not decreaseweb thickness. This web thickness testing demonstrated that no decreasein web thickness occurred and therefore solidity was preserved when aNWPM was corrugated in accordance with this invention.

Corrugated webs cannot be measured for web thickness using the LowPressure Thickness Gauge device described above. Thus, in these examplesanother technique (referred to as the Impregnation Method) was employedto determine the thickness of a corrugated web. The thickness of theflat webs of composite structures a and b and corrugated webs ofcomposite structures a' and b' shown in FIG. 12 were determined usingthe Impregnation Method by impregnating cut-out sections of the flatwebs and the composite structures that contained corrugated NWPM in alow viscosity resin, SCOTCHCAST Electrical Resin #8 (available from 3MCompany, St. Paul, Minn.). The resin was polymerized over a 24-hourperiod to freeze the corrugated web configuration. The flat andcorrugated web samples were then microtomed on the web edge to create anapproximately 0.1 mm thick cross-web profile of the web configuration.The corrugated samples were cut from selected areas of the compositestructure where securement points were not present to achieve a bettercomparison to the flat NWPM. The cut samples were then mounted on glassslides, illuminated, and magnified with an INFINIVAR Video InspectionMicroscope (available from Infinity Photo-Optical Company, Boulder,Colo.). Images were electronically captured with a CCD (charge coupleddevice) camera, and data was stored for image analysis. The imagingsystem was a QUANTIMET Model Q-570 Image Analyzer Model (available fromLeica Instruments, Deerfield, Ill.) having the capability to analyze theimage, determine the NWPM boundaries, and calculate NWPM thicknessregardless of the web pattern. Solidity was calculated from the webthickness.

This measurement procedure was completed for a minimum of two trials forthree samples of each structure. The data was averaged and is set forthin Table 5 as such.

                  TABLE 5                                                         ______________________________________                                                             Average Thickness                                                                          Average                                     Example  Structure   (mm) Per Layer                                                                             Solidity                                    ______________________________________                                        C-1      a           1.21         0.050                                       1        a'          1.25         0.048                                       C-2      b           0.92         0.055                                       2        b'          0.96         0.053                                       ______________________________________                                    

The data in Table 5 shows that there is no significant decrease in webthickness or increase in web solidity when the NWPM is corrugated usingthe method and apparatus of this invention. Indeed, the data shows thatweb thickness increased slightly and solidity decreased; however, theincrease in thickness and decrease in solidity is within theexperimental error. Accordingly, the loft of the NWPM is preserved.

Comparative Examples C-4 to C-8

The following comparative examples were conducted to demonstrate thedelicacy of nonwoven webs of polymeric microfiber and the deleteriouseffects that are incurred when such webs are compacted. In comparativeExamples C-5 to C-8, the nonwoven webs of polymeric microfiber werecompacted under various degrees of compressive stress. Example C-4 is anon-compacted control sample.

A 25.4 cm wide portion of the NWPM was cut into a number of 13.34 cmdiameter disks. The disks were weighed individually and stacked (5 disksper stack) with paper interleaves between each of the disks. The stackposition of each sample was maintained for data integrity. Samplethicknesses were measured using a 2.86 cm diameter circular flatbottomed pressure foot attached to a digital thickness gage capable ofdistance measurements accurate to 2×10⁻³ mm. The circular foot andmovable gage element combined to weigh 36 grams, resulting in ameasurement pressure of 5.5×10⁻³ bar.

In Comparative Examples C-5 through C-8, the NWPM samples werecompressed using a 10.16 cm inside diameter air cylinder actingvertically through a 12.7 cm diameter metal plate. Adjustment ofcompressive stress delivered through the plate onto the nonwoven webswas controlled by a standard air pressure regulator. Each NWPM samplewas held under the indicated compression for 30 minutes to compact thesample prior to evaluating the filtration performance of the NWPMsample. Thickness readings were taken prior to compaction, immediatelyfollowing compaction, and within approximately 10 minutes afterfiltration testing, and solidity was calculated therefrom. Filtrationtesting was performed approximately 10 minutes after compaction. TheNWPM samples were tested for particle penetration, and the results ofthe testing are reported in Table 6 as an average of five samples.

                                      TABLE 6                                     __________________________________________________________________________    Thickness, Solidity, and Filtration Performance of                            Nonwoven Webs of Polymeric Microfiber Subjected to Various Compressive        Stress                                                                                                            Filtration Results                                           Surface          Initial                                   Sample   Before Compression                                                                      Normal                                                                              After Compression                                                                        Pressure                                                                            Initial   After Filtration               Weight                                                                            Thickness                                                                          Solidity                                                                           Compression                                                                         Thickness                                                                           Solidity                                                                           Drop  Penetration                                                                             Thickness                                                                          Solidity             Example                                                                            (grams)                                                                           (cm) (Unitless)                                                                         (Bar) (cm)  (Unitless)                                                                         (mmH.sub.2 O)                                                                       (% NaCl)                                                                            Q   (cm) (Unitless)           __________________________________________________________________________    C-4* 0.804                                                                             0.081                                                                              0.077                                                                              0     0.081 0.077                                                                              5.0   8.04  0.51                                                                              0.081                                                                              0.077                C-5  0.844                                                                             0.093                                                                              0.070                                                                              1     0.063 0.104                                                                              7.2   4.54  0.43                                                                              0.074                                                                              0.089                C-6  0.768                                                                             0.090                                                                              0.066                                                                              2     0.055 0.108                                                                              7.3   6.11  0.39                                                                              0.063                                                                              0.095                C-7  0.796                                                                             0.090                                                                              0.069                                                                              3     0.049 0.126                                                                              8.7   5.22  0.34                                                                              0.062                                                                              0.100                C-8  0.816                                                                             0.080                                                                              0.079                                                                              4     0.044 0.144                                                                              9.8   5.18  0.31                                                                              0.055                                                                              0.115                __________________________________________________________________________     *Non-compacted control sample                                            

The data in Table 6 demonstrates that slight compressive stresses willcompact a NWPM, causing an increase in solidity and pressure drop and adecrease in the quality factor, Q. The compacted NWPM of ComparativeExamples C-15 through C-18 did not perform nearly as well as thenon-compacted NWPM of Comparative Example C-14.

Comparative Examples C-9 Through C-16

In these Examples, the NWPM was corrugated using a gear corrugatingmachine having identical 35.56 cm wide gears of 19.05 cm pitch circlediameter. The gear teeth were spaced at 0.3386 cm circular pitch. Thegear rolls were spaced from each other at an optimum partially meshingcondition to form a distinct corrugation pattern without crushing themicrofiber web more than necessary to achieve the corrugation pattern.The uppermost gear was held at 20° C. and the other gear at 79° C. usingtempered circulating water. As shown in Table 7, the peripheral speed ofboth gear rolls was adjusted between 3.05 and 21.34 meters per minute(mpm). The NWPM was passed through the meshing zone of the gears as theyrotated in opposite directions, forming a corrugated NWPM having aplurality of generally parallel and evenly spaced corrugations.

The corrugated structure of the NWPM was maintained by depositing spacedparallel strands of molten polypropylene (WRS-6, Lot 197, available fromShell Oil Co.) on the structure transverse to the parallel corrugationsat a center to center spacing of 0.25 cm. The polypropylene strands weredropped vertically downward from a spinning die at a temperature of 242°C. onto the peaks of the parallel corrugations. The polypropylenestrands were melt bonded to the corrugated NWPM and were allowed to coolunder ambient conditions.

Comparative Example C-16 is a flat, non-corrugated NWPM taken from thesame lot as Comparative Examples C-9 through C-15. Pressure drop andpenetration testing was performed as described above, the results ofwhich are reported in Table 7.

Example 4

In this Example, a NWPM taken from the same lot as Examples C-9 to C-16was corrugated as described in Example 1 to form a composite structurehaving the configuration a' shown in FIG. 12. The bonds to theshape-retaining means were sized so that the ESA of this compositestructure is approximately the same as the ESA of Examples C-9 to C-15.

                  TABLE 7                                                         ______________________________________                                        Comparison of a Corrugated Nonwoven Webs of Present Invention                 to Non-corrugated and Gear Corrugated Nonwoven Webs                                            Machine                                                                       Direction                                                                              Initial                                                    Strand    Process  Pressure                                                                             Initial                                             Diameter  Speed    Drop   Penetration                                  Example                                                                              (mm)      (mpm)    (mmH.sub.2 O)                                                                        (% NaCl)                                                                              Q                                    ______________________________________                                        C-9*   0.96      3.05     6.58   7.24    0.40                                 C-10*  0.68      6.10     6.46   6.90    0.41                                 C-11*  0.56      9.15     6.04   8.64    0.41                                 C-12*  0.48      12.20    5.54   8.80    0.44                                 C-13*  0.43      15.24    4.75   9.33    0.50                                 C-14*  0.38      18.29    5.12   8.94    0.47                                 C-15*  0.33      21.34    4.78   8.28    0.52                                 Average Values for C-9 to C-15                                                                  5.61     8.30      0.45                                     C-16**                    5.36   8.56    0.46                                 4                         4.52   5.36    0.65                                 ______________________________________                                         *Gear Corrugated Samples                                                      **Noncorrugated control sample                                           

The data set forth in Table 9 demonstrates that the Q factor for thecomposite structure of this invention (Example 4) is far superior to theQ factors for the gear corrugated samples (Examples C-9 to C-15). Thegear corrugated samples (average Q factor 0.45) demonstrated no gain infiltration performance over the non-corrugated sample (Q factor 0.46) ofthe same NWPM (Example C-16).

Examples 5-17

The purpose of these Examples is to show that composite structures ofthe invention can provide good thermal insulating properties.

The NWPM used in these Examples contained a mixture of microfibers andcrimped staple fibers. The NWPM was made as described in U.S. Pat. No.4,118,531 to Hauser. The NWPM contained 65 weight percent polypropylene(Fina 3860x, Houston, Tex.) microfiber and 35 weight percent polyesterstaple fibers (Hoechst Celanese, Charlotte, N.C.) that had a staplelength of about 3.81 cm (1.5 inches) and 6 denier per filament. Themicrofiber had an arithmetic median fiber diameter of approximately 7micrometers. The staple fibers had about 2.4 crimps per centimeter. Thecomposite structures were prepared as described in Examples 1-3. Asingle layer of CELESTRA nonwoven spunbond polypropylene fabric wasemployed as a shape-retaining means. Each composite structure had a sizeof 10 cm by 10 cm and was configured as outlined below in Table 8:

                  TABLE 8                                                         ______________________________________                                                 Basis Weight of                                                               NWPM          Number of                                                                              Corrugation                                   Example  (gm/m.sup.2)  Layers   Pitch (mm)                                    ______________________________________                                        5        40            1        9.52                                          6        40            2        9.52                                          7        40            3        9.52                                          8        40            1        4.76                                          9        40            2        4.76                                          10       40            3        4.76                                          11       100           1        9.52                                          12       100           2        9.52                                          13       100           3        9.52                                          14       100           1        4.76                                          15       100           2        4.76                                          16       200           1        9.52                                          17       200           1        4.76                                          ______________________________________                                    

The composite structures were tested for thermal resistance using aRapid-K™ test unit available from Dynatech R&D Company, Cambridge, Mass.The Thermal resistance measurements were conducted according to ASTMTest Method C518. The results of the thermal resistance tests are setforth in Table 9, where clo values are provided to illustrate thethermal resistance. Clo is defined mathematically as ##EQU4##

                  TABLE 9                                                         ______________________________________                                                              Thermal                                                           Basic Weight                                                                              Resistance                                                                             Clo Per Unit                                   Example No.                                                                             (g/m.sup.2) (Clo)    Weight (× 1000)                          ______________________________________                                         5        74          1.084    14.6                                            6        174         1.465    8.42                                            7        237         1.549    6.53                                            8        90          0.758    8.42                                            9        162         1.015    6.26                                           10        243         1.299    5.34                                           11        180         1.568    8.71                                           12        360         1.775    4.93                                           13        619         2.165    3.49                                           14        197         1.035    5.25                                           15        370         1.61     4.35                                           16        370         1.808    4.88                                           17        349         1.161    3.32                                           C-17.sup.a                                                                              207         0.624    3.01                                           C-18.sup.b                                                                              412         1.475    3.58                                           ______________________________________                                         .sup.a This sample was 3M commercial product Thinsulate ™ B200, which      is an embossed nonwoven web that has the same fiber composition as the        NWPM of Examples 5-17.                                                        .sup.b This sample was 3M commercial product Thinsulate ™ B400, which      is an embossed nonwoven web that has the same fiber composition as the        NWPM of Examples 5-17.                                                   

The data in Table 9 show that the thermal insulation of the inventioncan demonstrate good thermal resistance. The data also show that thethermal insulation of the invention can demonstrate better do values perunit weight than embossed products. A non-embossed, non-corrugatedsample would, in most instances, demonstrate better clo values per unitweight than the thermal insulation of the invention; however, the formerwould, as indicated in the Background, lack satisfactory web integrityto allow the web to be adhered to surface and to allow the web tomaintain a cohesive structure after being exposed to abrasion.

This invention may take on various modifications and alterations withoutdeparting from the spirit and scope thereof. Accordingly, it is to beunderstood that this invention is not to be limited to theabove-described, but it is to be controlled by the limitations set forthin the following claims and any equivalents thereof. It is also to beunderstood that this invention may be suitably practiced in the absenceof any element not specifically disclosed herein.

What is claimed is:
 1. A corrugating apparatus that comprises:(a) first and second paddles each attached at a first end to a means for moving the first and second paddles about a path, the first and second paddles extending radially from the moving means, and each paddle having a second end for supporting a web as the first and second paddles move about the path, the second ends of the first and second paddles being able to move towards each other to cause the web to corrugate; and (b) an ultrasonic welding device located downstream to where the paddles' second ends move towards each other, the ultrasonic welding device having a horn and an anvil, and the anvil includes the second ends of the first and second paddles.
 2. The apparatus of claim 1, wherein the means for moving the paddles about the path includes a flexible rubber belt that has a Shore A durometer in the range of 25 to
 90. 3. The apparatus of claim 1, wherein the apparatus has a first means for introducing the web to the corrugating apparatus and the path has a curved portion with a variable bend radius, the web being introduced to the corrugating apparatus on the curved portion of the path.
 4. The corrugating apparatus of claim 1 further comprising a means for altering the pitch of the paddles, the pitch altering means being located along the path adjacent to the ultrasonic welding device.
 5. The corrugating apparatus of claim 1, wherein the path has at least one curved portion and at least one straight portion.
 6. The method of claim 5, wherein the second ends of the paddles move towards each other to decrease pitch as the paddles move from the curved portion to the straight portion.
 7. The apparatus of claim 2, wherein the paddles are embedded in the flexible rubber belt such that an edge of the first end of the paddle is flush with the flexible rubber belt's inner surface.
 8. The apparatus of claim 7, wherein at least 70 percent of the total paddle length extends from the flexible rubber belt.
 9. The apparatus of claim 8, wherein at least 85 percent of the total paddle length extends from the flexible rubber belt.
 10. The apparatus of claim 2, wherein the flexible rubber belt is about 5 to 15 millimeters thick.
 11. The apparatus of claim 10, wherein the flexible rubber belt is 7 to 10 millimeters thick.
 12. The apparatus of claim 2, wherein the paddles are constrained in the flexible rubber belt to remain normal to a tangent of the flexible belt's path.
 13. The apparatus of claim 2, wherein the flexible rubber belt is made from silicone rubber.
 14. The apparatus of claim 2, wherein the flexible rubber belt is reinforced by running a plurality of parallel reinforcing members through the belt.
 15. The apparatus of claim 14, wherein the parallel reinforcing members are in the form of a plurality of chords.
 16. The apparatus of claim 14, wherein the parallel reinforcing members pass through openings in the paddles' first ends.
 17. The apparatus of claim 3, further comprising a second means for introducing a means for retaining the corrugated shape of the corrugated web, the second means causing the shape-retaining means to make contact with the corrugated web downstream to where it is corrugated.
 18. The apparatus of claim 17, wherein the first means includes a stationary guiding member that has a flared end and a curvature that corresponds to the arc created by the second ends of the paddles as they move about the path on the curved portion.
 19. The apparatus of claim 17, wherein the second means includes a bobbin.
 20. The apparatus of claim 17, including a member for supporting the flexible rubber belt at the location of the horn to allow ultrasonic signals from the ultrasonic welding device are absorbed by the corrugated web and the shape-retaining means.
 21. The apparatus of claim 1, wherein each paddle has a plurality of spaced energy concentrators on the paddles' second ends.
 22. The apparatus of claim 21, wherein the spaced energy concentrators are in the form of spaced protrusions on the paddle's second ends.
 23. The apparatus of claim 21, wherein the spaced energy concentrators on the first paddle's ends are offset from the spaced energy concentrators on the second paddle's ends.
 24. The apparatus of claim 22, wherein the protrusions have a top surface area of about 1 to 10 square millimeters.
 25. The apparatus of claim 24, wherein the protrusions have a top surface area of 2 to 6 square millimeters.
 26. The apparatus of claim 22, wherein the paddles are about 1 to 2 millimeters thick.
 27. The apparatus of claim 5, wherein the curved portion of the path has a varying bend radius that causes adjacent second ends of the first and second paddles to have a decreasing pitch in the direction of paddle movement.
 28. The apparatus of claim 2, wherein the flexible rubber belt is supported over a curved portion of the path on a module that includes a plurality of moveable substantially cylindrical members that support the belt and rotate about a longitudinal axis. 